1. Field of the Invention
The present invention relates to a method of relocating a plurality of files respectively with a different access frequency stored in a plurality of external storage units having different capacities and speeds with one another.
2. Description of Related Art
There are presently available a variety of storage units, for example an extended storage unit, a semiconductor disc, a magnetic disc, an optical disc library and an MT library. In the written order, these storage units operate at higher speeds but have less capacities and are more expensive.
For configuring a computer system, all or a part of the above-mentioned storage units are combined and hierarchically arranged in accordance with the access speed. When such a system is actually operated, it is necessary to relocate files frequently among different storage units from a viewpoint of utilizing efficiency.
In a conventional file relocating method, for example, as described in JP-A-63-80344, files are relocated in external storage units having higher access speeds in the descending order in which the files are more frequently subjected to physical input and output accesses. More specifically, data indicating the frequency of physical input and output accesses is stored in a table by a monitor program, and the data in this table is sorted in the descending order of the physical input and output frequencies. In accordance with the sorting result, files most frequently accessed for physical input and output are copied and relocated in faster external storage units. On the other hand, files with less physical input and output frequencies are copied and relocated in slower external storage units. This relocation technique results in an extreme reduction of human manipulation and a rapid and precise relocation of files in external storage units, thereby resulting in improving the access efficiency of the files.
Conventional file relocating methods including the above described one, however, may imply the following problems.
(i) Attention is hardly given to an execution time of a job expected by a user, so that a problem arises when a high speed execution is desired to a job which less frequently accesses files physically.
(ii) Attention is hardly given to a time necessary for a relocation of files and concentration of accesses to a particular external storage unit due to the relocation. For this reason, problems are encountered when files must be relocated in destination storage units within a limited time and when a particular external storage unit is highly frequently accessed to frequently cause a storage unit waiting time.
(iii) The file capacity is not considered. For example, a highly frequently accessed file requiring a large capacity is dedicatedly allocated in a storage unit having a relatively small capacity and high speed only by reason of its being highly frequent accessed, whereas, a group of files frequently accessed next to the above-mentioned file but each requiring far smaller capacities than the same are allocated in a low speed and large capacity storage unit, thereby causing a problem that a file access efficiency of the whole system is degraded.
(iv) A determination basis for determining relocating destination storage units of files in a storage hierarchy constituted by a plurality of kinds of storage units which respectively have different access capabilities is not distinguished from a determination basis for determining relocating destination storage units so as to balance access loads to the respective storage units among a plurality of storage units having the identical access capability.